VICTORIA, Texas -- A chartered bus coming from Mexico veered off a highway early Wednesday and overturned, killing one passenger and injuring dozens of others, at least six of them critically, authorities said.

Some of the passengers crawled out an emergency exit on the roof.

The bus had left Monterrey, Mexico, on Tuesday evening and was headed to Houston when it crashed on U.S. 59 several hours before dawn, authorities said.

"The investigation is centering on driver fatigue," said Tom Vinger, spokesman for the Texas Department of Public Safety. "It looks like he ran off the road, way overcorrected then tipped over on the passenger side."

Passenger Francisco Cardenas, 66, who was returning from a holiday in Monterrey, said he was awakened by screams.

"The hardest thing was to see all the other people," said Cardenas, who had a cut on his face, blood on his shirt and blood on his shoes. "There was no way out."

He said people eventually pushed the emergency exit on the roof to escape.

After the bus ended up on its side, it was struck by a small pickup truck, Vinger said. The driver of the truck was not injured.

The bus was operated by Capricorn Bus Lines Inc. of Houston. Francisca Flores, manager of the family-owned company, said it has four buses and only makes trips between Houston and Monterrey. She said 47 people were on the bus but declined to elaborate, beyond saying it was the first wreck in the company's nine-year history.

The identity of the man who was killed was not immediately released.

Vinger said the driver was not seriously injured, and that it was too early to tell whether he could face charges. His name was not released.

In a separate bus accident Wednesday, a Greyhound bus collided with a tractor-trailer near Henderson, N.C., and at least 50 people were taken to hospitals, two of them in critical condition, hospital and Highway Patrol officials said.

The Greyhound bus was following the truck on U.S. 1 and failed to slow down when the truck made a left turn, said patrol Sgt. Steve Green. The bus ran off the right shoulder and down an embankment, and tipped onto its side.

The bus, operated by Greyhound subsidiary Carolina Trailways, was on a regularly scheduled travel route from Richmond, Va., to Raleigh, said Carolina Trailways general manager Elvis Latiolais.

The Greyhound driver was flown to a hospital but the severity of his injuries was unclear, Green said. The driver of the tractor-trailer was not injured. None of the injured passengers had life-threatening injuries, said David Ruggles, spokesman for Maria Parham Medical Center in Henderson.

In the Texas wreck, there were 46 people aboard the bus and another who died at the scene. Twenty-six people were treated and released from hospitals in Victoria.

Eleven were hospitalized with non-life-threatening injuries. Five others were in intensive care units. One person had to have an arm amputated.

At least four others were transferred to hospitals in San Antonio, where one was in critical condition.

Victoria is about 125 miles southwest of Houston and 110 miles southeast of San Antonio.

Associated Press writers Monica Rhor in Houston and Elizabeth White in San Antonio contributed to this report.